The present invention relates to frequency converting mixer circuits for use in tuners of satellite broadcasting receivers, television sets, and the like, and particularly relates to mixer circuits suitable for integrated circuits.
A conventional mixer circuit used in a tuner using an integrated circuit is constituted by a mixer circuit for UHF-band signals, a mixer circuit for VHF-band signals, and a mixer circuit for hyper-band signals, as described in IEEE "Transactions on Consumer Electrons", Vol. CE-32, No. 4, November 1986, pp. 723-732.
FIG. 22 shows the conventional mixer circuit as described in the aforementioned literature. In FIG. 22, a block A surrounded by a broken line represents a double-balanced mixer circuit for receiving a hyper-band signal, a block B surrounded by a broken line represents a buffer amplifier circuit for amplifying the hyper-band signal, a block C surrounded by a broken line represents a double-balanced mixer circuit for receiving a VHF band signal, and a block D surrounded by a broken line represents a buffer amplifier circuit for amplifying the VHF band signal.
In the aforementioned conventional receiver, a plurality of mixer circuits must be provided separately corresponding to the signal bands to be received. Accordingly, the circuits are large in size and as well as in electric power consumption. Further, switching circuits complex in construction must be used for switching the functions of those circuits.